The invention relates to a self-attaching fastener and more particularly to a threaded fastener, mounting pin or shaft, or other item that is forcibly mechanically interlocked with, or clinchingly attached to, a portion of a sheet material item. The invention also involves an apparatus and a method for forming such an attachment. Such attachment is accomplished in some embodiments without shearing the sheet material item in order to form a leakproof attachment of the fastener.
It is frequently desirable to secure objects to a member formed from a relatively thin sheet material, such as sheet metal, deformable sheet plastics, or other such sheet materials. Because such sheet materials are generally too thin to form adequate threaded holes therein by drilling and tapping, threaded male or female fasteners are frequently welded or otherwise secured to such sheet materials.
In this regard, reference is made to U.S. Pat. Nos. 4,574,453 and 4,574,473, both of which are assigned to the same assignee as the present invention, wherein a method and an apparatus for securing a fastener to a sheet material item are disclosed and claimed. Both of these patents are hereby incorporated by reference herein. The method and apparatus of such patents both involve forcing the fastener or a portion thereof into the sheet material in a manner by which a part of the sheet material is sheared, and an interlocking attachment or connection is made between the fastener and the sheet material. As a result, the attachment formed by such method and apparatus does not result in a leakproof attachment of at least a male threaded fastener to a sheet material item.
The present invention overcomes this disadvantage by allowing fasteners to be attached or secured to a sheet material member without shearing the sheet material at all in some embodiments, thereby providing for such an attachment in areas where a leakproof assembly is necessary or desirable, such as in the production of items that are used to contain fluids, for example. In other embodiments, where shearing is necessary or desirable, such shearing occurs in an area of the joint that does not involve the interlock between the sheet material and the fastener or other item.
According to the present invention, a fastener having an attachment portion with a lateral face and a transverse edge thereon is attached to either a single or multiple layer sheet material item. The apparatus and method for forming such an attachment preferably involves a pair of die means movable relative toward one another in a generally longitudinal direction, with a first of the die means including a number of die members or segments defining an opening therebetween for receiving a punch or ram on the other die means. The die members are generally laterally movable relative to one another, with an anvil being disposed within, and forming the bottom of, the opening.
A press is provided for forcibly moving the die means generally longitudinally (axially) toward one another (with the attachment portion of the fastener and the sheet material disposed therebetween) in order to force the attachment portion and a portion of the sheet material into the opening between the die members without shearing the sheet material, at least in the area of interlocking attachment. The attachment portion and a first part of the sheet material portion are pressed or squeezed generally longitudinally by the punch or ram into the opening and against the anvil in order to compress or laterally deform part of the sheet material portion (and in some cases the attachment portion) outwardly in order to form a longitudinal clinching interlock between the attachment portion and the sheet material. The die members, however, are resiliently biased laterally toward one another, and are forced laterally outwardly away from one another in response to such lateral outward deformation of the sheet material portion.
Preferably the transverse edge of the attachment portion of the fastener includes a surface discontinuity formed by knurling, for example, and a second part of the sheet material portion is forcibly urged into an interlocking engagement with such surface discontinuity. In some embodiments of the present invention, the attachment portion of the fastener is generally conical in shape, with the transverse edge being tapered outwardly in a direction toward the sheet material. In such embodiments, the second part of the sheet material portion is forcibly urged generally laterally inwardly to engage the tapered, transverse edge of the fastener attachment portion in order to form the above-mentioned interlock.
Furthermore, in other embodiments of the present invention, the attachment portion of the fastener can include a recessed area on the lateral face oriented toward the sheet material, and the above-mentioned first part of the sheet material portion is forcibly urged into such recessed area as it is being laterally deformed. The apparatus and method according to the present invention preferably includes the use of a stripper device for holding the interlocked fastener and sheet material portion substantially in contact or in engagement with the die members of the first die means while the second die means is moved longitudinally away after the fastener is attached to the sheet material.
Although the above-described apparatus, with laterally movable die members or segments, is the preferred apparatus for forming the joint or attachment of the present invention, alternate die apparatuses can also be employed. Such alternate apparatuses include those having a first die means that is solid (or non-segmented), and thus does not have laterally movable die members or segments, with the other die means including a punch or ram relatively movable in a longitudinal direction with respect to the first die means in a manner generally as described above. In such examples, the opening in the solid first die means must have outwardly tapered side walls, or at least walls that are parallel to the longitudinal axis, in order to allow the formed joint or attachment to be removed from the first die means. One skilled in the art will readily recognize from the following discussion that although the preferred apparatus described herein provides distinct advantages in forming the attachment or joint of the invention, other solid or laterally displaceable first die means can alternately be used.
Additional objects, advantages, and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.